Ultrahigh Time Resolution Research Articles

Investigation of fabric tactile perception using the event-related potential method

The mechanism of the neuro-electrophysiological response of the human brain to skin tactile stimulation has always been an important research topic in the field of comfort perception of textile materials. In order to explore the characteristic neural potential components induced by various fabric tactile stimulation and their influence rules, event-related potential technology with ultra-high time resolution was introduced to monitor the somatosensory brain region under tactile stimulation of fabrics with different tactile properties, and the signal changes of related potentials were extracted and analyzed. The results showed that the amplitudes of N100 increased with the stiffness of the fabric, the amplitudes of P200 decreased with the smoothness of the fabric, and the amplitudes of P300 decreased with the smoothness and softness of the fabric. These results indicated that N100, P200, and P300 potentials could be used as neurophysiological response indexes of brain neurons to distinguish the subtle differences in fabric tactile properties. This finding not only laid a scientific theoretical basis for the brain perception mechanism of fabric tactile properties, but also provided a possibility for further quantification characterization of textile comfort perception.

Timing Estimation and Limits in TOF-PET Detectors Producing Prompt Photons.

The production of prompt photons providing high photon time densities is a promising avenue to reach ultrahigh coincidence time resolution (CTR) in time-of-flight PET. Detectors producing prompt photons are receiving high interest experimentally, ignited by past exploratory theoretical studies that have anchored some guiding principles. Here, we aim to consolidate and extend the foundations for the analytical modeling of prompt generating detectors. We extend the current models to a larger range of prompt emission kinetics where more stringent requirements on the prompt photon yield rapidly emerge as a limiting factor. Lower bound and estimator evaluations are investigated with different underlying models, notably by merging or keeping separate the prompt and scintillation photon populations. We further show the potential benefits of knowing the proportion of prompt photons within a detection set to improve the CTR by mitigating the detrimental effect of population (prompt vs scintillation) mixing. Taking into account the fluctuations on the average number of detected prompt photons in the model reveals a limited influence when prompt photons are accompanied by fast scintillation (e.g., LSO:Ce:Ca) but a more significant effect when accompanied by slower scintillation (e.g., BGO). Establishing performance characteristics and limitations of prompt generating detectors is paramount to gauging and targeting the best possible timing capabilities they can offer.

Measurement of transient temperature using laser-induced breakdown spectroscopy (LIBS) with the surface temperature effect

A method based on LIBS technology for measuring transient surface temperatures had been proposed with an ultra-high time resolution of several μs.

Jitter enhanced full digital RF transmitter and PWM RFPA for 5G broadband communications

RFPA (radio frequency power amplifier) based on PWM (pulse width modulation) can be perfect linear without using complicated DPD (digital pre-distortion) hardware. However, PWM RFPA need ultra-high PWM time resolution (less than 10 ps) for wide-band 5G, which is limited by CMOS technologies (can reach 40 ps). It limits the complexity of modulation so that PWM RFPA cannot be really commercialized so far in wideband radio/mobile technologies. This paper presents our contribution by introducing jitter into PWM. For the first time, we demonstrate that jitter can improve the PWM time resolution equivalently reaching less than 2.6 ps. Hence PWM RFPA can be used in 5G supporting 256QAM OFDM modulation based on currently available digital CMOS technologies. We demonstrate that jitter can refine the inherent resolution of PWM hardware circuit modulation. The jitter makes the MCS (modulation and coding scheme) of the bandwidth OFDM system improved from 16QAM to 256QAM in the band n28 of 3GPP 38.101. We also verified that 5G 256QAM OFDM modulation is achievable in the 3GPP band n20, Softbank band28 and NTT Docomo band28. The RMS EVM (root mean square error vector magnitude) of 256QAM OFDM modulation is about −44 dB.

Development of high rate and ultrahigh time resolution MRPC for the future time of flight systems

This paper reports a 32-gap MRPC built with very thin and low resistivity glasses aiming at a high rate and ultrahigh time resolution. Fast amplifier and waveform digitization systems are employed to achieve a better resolution. This MRPC, with 128 μm thick gaps, reaches a 98% efficiency at 13.3 kV and a time resolution of 16 ps during the cosmic tests. Moreover, we have performed X-ray tests at different particle fluxes. At a rate of 15 kHz/cm2, the efficiency is still above 95% and a time resolution of 20 ps is achieved, which would fulfill the requirements of SoLID ToF system.

Preparation of CsPbBr<sub>3</sub> perovskite nanocrystals with controllable morphology and <i>in-situ</i> photoluminescence of formation kinetics

Cesium-lead halide perovskite nanocrystals (CsPb<i>X</i><sub>3</sub> (<i>X</i> = Br, Cl, I) PNCs) have become ideal luminescent materials for wide color gamut display devices, white LED lighting and high-efficiency solar cells, due to adjustable energy band gap, high fluorescence quantum yield, narrow fluorescence emission peak, and ultra-high defect tolerance. The preparation of CsPb<i>X</i><sub>3</sub> PNCs with controllable size and morphology is a prerequisite for obtaining efficient and stable photovoltaic/photovoltaic devices. In this report, the CsPbBr<sub>3</sub> PNCs with different shapes are prepared by adding different concentrations of dodecanedioic acid (DDDA) ligands at room temperature through using ligand-assisted reprecipitation method. Utilizing the X-ray diffractometer, transmission electron microscopy, ultraviolet spectrophotometer, fluorescence spectrometers (PL), the phase structure, microstructure and optical properties of the nanocrystals are investigated. The results show that the presence of DDDA ligands have no influence on the phase structure of nanocrystal products, they all present a cubic phase structure. Surprisingly, the morphology of the nanocrystals gradually transforms from nanocubes into nanoplatelets with ～5 layers in thickness as the concentration of DDDA increases. In addition, the PL spectrum shows a significant blue shift from 509 nm to 478 nm. By using the <i>in-situ</i> homemade PL device with ultra-high time resolution (～100 ms), the real-time monitoring PL spectra of nanocrystals in the formation process are measured. The results demonstrate that nanocrystals undergo rapid nucleation and focusing of size distribution growth to generate nanocubes in the absence of DDDA ligand. When the DDDA ligand is present, nanocrystals are mainly nanoplatelets in the early growth stage due to the decelerated reaction. As the reaction proceeds, nanocubes can emerge and grow gradually while the nanoplatelets disappear when the concentrations of DDDA ligands are 25% and 50%. As the concentration is further increased to 75%, almost nanoplatelets could be formed after the nucleation stage and growth stage. Unexpectedly, preformed nanoplatelets are unstable for the prolonged reaction time as a result of the high surface energy, and they will eventually transform into isotropic nanocubes through dissolution-recrystallization pathway, indicating that the process in the later stage is controlled mainly by thermodynamics. Our findings offer an efficient strategy to synthesize the perovskite nanocrystals with controllable size and morphology.

Experimental evidence of runaway electron tail generation via localized helical structure in pellet-triggered tokamak disruptions

A novel detector, using stacked BGO crystals, is developed for runaway electron (REs) studies in the DIII-D tokamak. It is able to resolve fast dynamics of high-energy tail formation of REs with an ultra-high time resolution of ∼1 μs. As a cost, the detector estimates the ‘effective’ energy of a given shape of γ-ray spectra and sacrifices the energy resolution. In aid of the new measurement capability, a rapid, inhomogeneous growth of RE tail is observed in detail during a major disruption triggered by an argon pellet. It is found that both the population and energy of a well-confined RE tail significantly oscillate at the early period of the growth. The oscillation phase is locked to a slow rotating magnetohydrodynamic instability, which is briefly destabilized for only ∼1 ms at the early period of the current quench. The oscillation ceases promptly, when the mode disappears. The data suggests that the high-energy RE tail is well-confined and accelerated via a localized helical structure in the plasma core.

Ultrafast extreme ultraviolet photoemission electron microscope.

Here, we report our newly built table-top ultrafast extreme ultraviolet (EUV) photoemission electron microscope. The coherent ultrafast EUV light is served by a single order harmonic, which is generated by the interaction between the intense 800-nm femtosecond laser and noble gases in the hollow core fiber. The required order of the harmonic is selected out by a single grating in the off-plane mount and focused on the sample in the ultrahigh vacuum chamber of the photoemission electron microscope. Using metal gold and copper samples, the spatial resolution is calibrated to be better than 50nm and the energy resolution is calibrated to be better than 300 meV. This microscope provides an advanced tool for studying electron dynamics covering the full Brillouin zone of solid materials with ultrahigh time, space, and energy resolution.

Tabletop X-ray spectroscopy probes electron dynamics on attosecond timescales

Ultrahigh time resolution tabletop X-ray spectroscopy is poised to further understanding of quantum materials, light harvesting devices, and ultrafast electronics.

High time resolution measurements of droplet evaporation kinetics and particle crystallisation.

A refined technique for observing the complete evaporation behaviour of free-falling droplets, from droplet generation to complete solvent evaporation, with ultra-high time resolution is introduced and benchmarked. High-resolution phase-delay stroboscopic imaging is employed to simultaneously resolve the evolving droplet morphology, geometric and aerodynamic diameters, throughout the evaporative lifetime with a user-controlled < μs timescale. This allows rapid, complex morphological changes, such as crystallisation events, to be clearly observed and the corresponding mechanisms to be inferred. The dried particles are sampled for offline SEM analysis and the observed morphologies compared to the inflight imaging. Density changes can be calculated directly from the deviation between the geometric and aerodynamic diameters. The full capabilities of the new technique are demonstrated by examination of the different evaporation behaviours and crystallisation mechanisms for aqueous sodium chloride droplets evaporating under different ambient relative humidity (RH) conditions. The crystallisation window, defined as the time taken from initial to complete crystallisation, is shown to be RH dependent, extending from 0.03 s at 20% RH and 0.13 s at 40% RH. The different crystallisation mechanisms observed during the experiments are also clearly reflected in the final structure of the dry particles, with multi-crystal structures produced at low RH compared to single-crystal structures at higher RH. It is anticipated that this technique will unlock measurements which explore the evaporation behaviour and crystallisation mechanisms for rapid, complex droplet drying events, and with increasingly non-ideal solutions, relevant to industrial applications.

Zero-Dimensional MXene-Based Optical Devices for Ultrafast and Ultranarrow Photonics Applications.

In recent years, MXene has become a hotspot because of its good conductivity, strong broadband absorption, and tunable band gap. In this contribution, 0D MXene Ti3C2Tx quantum dots are synthesized by a liquid exfoliation method and a wideband nonlinear optical response from 800 to 1550 nm is studied, which have a larger nonlinear absorption coefficient β of –(11.24 ± 0.14) × 10–2 cm GW–1. The carrier dynamic processes of 0D MXene are explored with ultrahigh time resolution nondegenerate transient absorption (TA) spectroscopy, which indicates that the TA signal reaches its maximum in 1.28 ps. Furthermore, 0D MXene is used to generate ultrashort pulses in erbium or ytterbium‐doped fiber laser cavity. High signal‐to‐noise (72 dB) femtosecond lasers with pulse durations as short as 170 fs with spectrum bandwidth of 14.8 nm are obtained. Finally, an ultranarrow fiber laser based on 0D MXene is also investigated and has a full width at half maximum of only 5 kHz, and the power fluctuation is less than 0.75% of the average power. The experimental works prove that 0D MXene is an excellent SA and has a promising application in ultrafast and ultranarrow photonics.

Shining Emitter in a Stable Host: Design of Halide Perovskite Scintillators for X-ray Imaging from Commercial Concept.

Halide perovskite (HP) nanocrystals (NCs) have recently shown great potential for X-ray detection and imaging. However, the practical application still has a long way to go with many technical requirements waiting to be fulfilled, including structure optimization, stability enhancement, and cost reduction. A design principle in this beginning stage is urgently needed but still lacking. Herein, with an "emitter-in-matrix" principle refined from commercial scintillators, CsPbBr3@Cs4PbBr6 with emissive CsPbBr3 NCs embedded inside a solid-state Cs4PbBr6 host is subjected to X-ray sensing and imaging. The Cs4PbBr6 matrix not only enhances the attenuation of X-rays but also dramatically improves the stability of CsPbBr3 NCs. A favorable optical design with the Cs4PbBr6 matrix being transparent to the emission from CsPbBr3 NCs enables efficient light output. As a result, stable and sensitive scintillation response to X-ray signals is demonstrated with superior linearity and ultrahigh time resolution. In order to show the huge potential for practical applications, X-ray imaging using a large-area film (360 mm × 240 mm) by the blade-coating technique is carried out to obtain a high-quality image of interior structures invisible to the human eye. In addition to the above advantages in optics, CsPbBr3@Cs4PbBr6 also enjoys facile solution synthesis with large scalability, excellent repeatability, and low cost.

Timing-performance evaluation of Cherenkov-based radiation detectors

With the upgradation of detector components, such as scintillators and photodetectors, the PET-image signal-to-noise ratio of time-of-flight positron emission tomography (TOF-PET) systems has been improved, compared to those of ordinary nonTOF-PET systems. A TOF-PET with an ultrahigh time resolution, for example a coincidence time resolution (CTR) better than few tens of picoseconds, can not only improve the image quality, but also remove the image reconstruction process, significantly impacting medical imaging. Therefore, it is crucial to develop a high-time resolution PET detector. We focus on the prompt emission of Cherenkov radiation, owing to the instantaneousness of which, a high time resolution can be expected. One of the candidates for the Cherenkov radiator is lead fluoride (PbF2) due it has excellent properties, including transparency toward the ultraviolet region, high refractive index (n = 1.82), and high density (7.77 g/cm3). Moreover, it does not contain radioisotopes, unlike lutetium-based scintillators, which are commonly used in the currently available TOF-PET detectors. In this work, we experimentally investigate the timing performance of PbF2-based Cherenkov detectors, breaking down the timing performance into physical components. 3×3×5 mm3 and 9.6×9.6×5 mm3 PbF2 crystals are used as Cherenkov radiators; both are attached to a microchannel plate photomultiplier tube (MCP-PMT) because the single channel MCP-PMT is one of the best photodetectors in terms of the SPTR, which is 25 ps full width at half maximum (FWHM). All the surfaces, except the end surface where the MCP-PMT is connected, are wrapped in black tape to suppress the reflections of the Cherenkov photons in the crystal. The CTR is measured by placing a detector pair face-to-face, using an 22Na point source, and an oscilloscope at 20 GS/s with a set bandwidth of 4.2 GHz. A CTR of 46.9 ps FWHM, corresponding to a position resolution of 7.0 mm, is obtained, consistent with our simulation results.

Simple and ultrafast resonance frequency and dissipation shift measurements using a fixed frequency drive

A new method for determination of resonance frequency and dissipation of a mechanical oscillator is presented. Analytical expressions derived using the Butterworth-Van Dyke equivalent electrical circuit allow the determination of resonance frequency and dissipation directly from each impedance datapoint acquired at a fixed amplitude and frequency of drive, with no need for numerical fitting or measurement dead time unlike the conventional impedance or ring-down analysis methods. This enables an ultrahigh time resolution and superior noise performance with relatively simple instrumentation. Quantitative validations were carried out successfully against the impedance analysis method for inertial and viscous loading experiments on a 14.3 MHz quartz crystal resonator (QCR). Resonance frequency shifts associated with the transient processes of quick needle touches on a thiol self-assembled-monolayer functionalised QCR in liquid were measured with a time resolution of 112 μs, which is nearly two orders of magnitude better than the fastest reported quartz crystal microbalance. This simple and fast fixed frequency drive (FFD) based method for determination of resonance frequency and dissipation is potentially more easily multiplexable and implementable on a single silicon chip delivering economies of scale.

Ultralow Noise Optical Frequency Combs

The invention of optical frequency combs (OFCs) based on femtosecond (fs) mode-locked lasers has merged laser based spectroscopy with fs-laser technology. OFCs have triggered quantum leaps of advancement in photonics, physics, astronomy, and engineering, while also lending themselves to applications in medical and environmental fields. The key feature of OFCs is their ultrahigh frequency and time resolution. In this review, we introduce the concept behind OFCs and their sources, with a focus on stability and phase-noise performance. We conclude with a discussion of recent progress of a monolithic OFC, which provides ultralow free-running phase noise and an unprecedented frequency stability of 1 part in ${10^{19}}$ at a 1 s gate time.

Room temperature optical mass sensor with an artificial molecular structure based on surface plasmon optomechanics

We propose an optical weighing technique with a sensitivity down to a single atom through the coupling between a surface plasmon and a suspended graphene nanoribbon resonator. The mass is determined via the vibrational frequency shift on the probe absorption spectrum while the atom attaches to the nanoribbon surface. We provide methods to separate out the signals of the ultralow frequency vibrational modes from the strong Rayleigh background, first based on the quantum coupling with a pump-probe scheme. Owing to the spectral enhancement in the surface plasmon and the ultralight mass of the nanoribbon, this scheme results in a narrow linewidth (∼GHz) and ultrahigh mass sensitivity (∼30 yg). Benefitting from the low noises, our optical mass sensor can be achieved at room temperature and reach ultrahigh time resolution.

How do reference montage and electrodes setup affect the measured scalp EEG potentials?

Objective. Human scalp electroencephalogram (EEG) is widely applied in cognitive neuroscience and clinical studies due to its non-invasiveness and ultra-high time resolution. However, the representativeness of the measured EEG potentials for the underneath neural activities is still a problem under debate. This study aims to investigate systematically how both reference montage and electrodes setup affect the accuracy of EEG potentials. Approach. First, the standard EEG potentials are generated by the forward calculation with a single dipole in the neural source space, for eleven channel numbers (10, 16, 21, 32, 64, 85, 96, 128, 129, 257, 335). Here, the reference is the ideal infinity implicitly determined by forward theory. Then, the standard EEG potentials are transformed to recordings with different references including five mono-polar references (Left earlobe, Fz, Pz, Oz, Cz), and three re-references (linked mastoids (LM), average reference (AR) and reference electrode standardization technique (REST)). Finally, the relative errors between the standard EEG potentials and the transformed ones are evaluated in terms of channel number, scalp regions, electrodes layout, dipole source position and orientation, as well as sensor noise and head model. Main results. Mono-polar reference recordings are usually of large distortions; thus, a re-reference after online mono-polar recording should be adopted in general to mitigate this effect. Among the three re-references, REST is generally superior to AR for all factors compared, and LM performs worst. REST is insensitive to head model perturbation. AR is subject to electrodes coverage and dipole orientation but no close relation with channel number. Significance. These results indicate that REST would be the first choice of re-reference and AR may be an alternative option for high level sensor noise case. Our findings may provide the helpful suggestions on how to obtain the EEG potentials as accurately as possible for cognitive neuroscientists and clinicians.

A dynamic monitoring approach for the surface morphology evolution measurement of plasma facing components by means of speckle interferometry.

Plasma Facing Components (PFCs) in a magnetically confined fusion plasma device will be exposed to high heat load and particle fluxes, and it would cause PFCs' surface morphology to change due to material erosion and redeposition from plasma wall interactions. The state of PFCs' surface condition will seriously affect the performance of long-pulse or steady state plasma discharge in a tokamak; it will even constitute an enormous threat to the operation and the safety of fusion plasma devices. The PFCs' surface morphology evolution measurement could provide important information about PFCs' real-time status or damage situation and it would help to a better understanding of the plasma wall interaction process and mechanism. Meanwhile through monitoring the distribution of dust deposition in a tokamak and providing an upper limit on the amount of loose dust, the PFCs' surface morphology measurement could indirectly contribute to keep fusion operational limits and fusion device safety. Aiming at in situ dynamic monitoring PFCs' surface morphology evolution, a laboratory experimental platform DUT-SIEP (Dalian University of Technology-speckle interferometry experimental platform) based on the speckle interferometry technique has been constructed at Dalian University of Technology (DUT) in China. With directional specific designing and focusing on the real detection condition of EAST (Experimental Advanced Superconducting Tokamak), the DUT-SIEP could realize a variable measurement range, widely increased from 0.1 μm to 300 μm, with high spatial resolution (<1 mm) and ultra-high time resolution (<2 s for EAST measuring conditions). Three main components of the DUT-SIEP are all integrated and synchronized by a time schedule control and data acquisition terminal and coupled with a three-dimensional phase unwrapping algorithm, the surface morphology information of target samples can be obtained and reconstructed in real-time. A local surface morphology of the real divertor tiles adopted from EAST has been measured, and the feasibility and reliability of this new experimental platform have been demonstrated.

An evaluation of the various aspects of the progress in clinical applications of laser driven ionizing radiation

There has been a vast development of laser-driven particle acceleration (LDPA) using high power lasers. This has initiated by the radiation oncology community to use the dose distribution and biological advantages of proton/heavy ion therapy in cancer treatment with a much greater accessibility than currently possible with cyclotron/synchrotron acceleration. Up to now, preclinical experiments have only been performed at a few LDPA facilities; technical solutions for clinical LDPA have been theoretically developed but there is still a long way to go for the clinical introduction of LDPA. Therefore, to explore the further potential bio-medical advantages of LDPA has pronounced importance. The main characteristics of LDPA are the ultra-high beam intensity, the flexibility in beam size reduction and the potential particle and energy selection whilst conventional accelerators generate single particle, quasi mono-energetic beams. There is a growing number of studies on the potential advantages and applications of Energy Modulated X-ray Radiotherapy, Modulated Electron Radiotherapy and Very High Energy Electron (VHEE) delivery system. Furthermore, the ultra-high space and/or time resolution of super-intense beams are under intensive investigation at synchrotrons (microbeam radiation and very high dose rate (> 40 Gy/s) electron accelerator flash irradiation) with growing evidence of significant improvement of the therapeutic index. Boron Neutron Capture Therapy (BNCT) is an advanced cell targeted binary treatment modality. Because of the high linear energy transfer (LET) of the two particles (7Li and 4He) released by 10BNC reaction, all of the energy is deposited inside the tumour cells, killing them with high probability, while the neighbouring cells are not damaged. The limited availability of appropriate neutron sources, prevent the more extensive exploration of clinical benefit of BNCT. Another boron-based novel binary approach is the 11B-Proton Fusion, which result in the release of three high LET alpha particles. These promising, innovative approaches for cancer therapy present huge challenges for dose calculation, dosimetry and for investigation of the biological effects. The planned LDPA (photons, VHEE, protons, carbon ions) at ELI facilities has the unique property of ultra-high dose rate (> Gy/s−10), short pulses, and at ELI-ALPS high repetition rate, have the potential to develop and establish encouraging novel methods working towards compact hospital-based clinical applications.

A demonstration of ultra-high time resolution with a pulse-dilation photo-multiplier

A novel microchannel plate (MCP) intensified high-speed photo-multiplier tube making use of pulse-dilation[1] has been tested. A ramped photo-cathode voltage followed by a relatively long drift region results in a transit time which is dependent on the photo-electron birth time. This leads to temporal magnification or dilation, so providing an enhancement in time resolution of the optical signal with respect to the electrical signal at the output anode. By this means a time resolution on the order of picoseconds may be realized with a substantially slower oscilloscope. The photo-electron signal is guided from a photo-cathode to an MCP by an axial magnetic field and a short input record length is stretched by a factor up to 40X to yield significantly improved time resolution at the photo-cathode. Results of the first measurements are presented.